1. Field of the Invention
Aromatic polyimides (PI) are usually thought as being high temperature, high performance plastics that require processing via a poly(amic acid) precursor. This is because polyimides, especially those based on PMDA or BTDA, are usually insoluble in most organic solvents and are either infusible or have very high melting or softening temperatures near that at which decomposition begins. Hence, there exists a need for polyimides for matrix resins and adhesives that exhibit enhanced flow during processing.
2. Prior Art
A patent has recently been granted to St. Clair and Burks (U.S. Pat. No. 4,444,979) for preparing polyphenylene ethers with imide linking groups that are melt processable in the 250.degree.-390.degree. C. range. Other patents also teach the incorporation of ether or sulfide linkages into a polyimide backbone (Williams, III, U.S. Pat. No. 3,933,749 and U.S. Pat. No. 3,983,093 and Takekoshi, U.S. Pat. No. 4,281,100). By diluting the imide ring in the backbone with arylene ether groups, melt processability was improved. Unfortunately, the resulting polymers lack resistance to chlorinated organic solvents.
Plastic materials are routinely mixed with additives to improve such properties as melting temperature, melt flow, flexibility, and elastic modulus, i.e., to improve the processability while not altering the chemical nature of the macromolecule. ("Plastics Additives Handbook," R. Gachter and H. Muller, 2nd ed., 1983, p. 251, Hanser Publishers, New York). Such additives often lower desirable properties such as thermooxidative stability, glass transition temperature and tensile strength. In addition, low molecular weight additives frequently migrate to the surface of the plastic material and impart a characteristic odor, an oily feeling, or other undesirable properties to the material.
Accordingly, the primary object of the present invention is the preparation of melt processable polyimides that maintain desirable polymer properties. This is done by adding small amounts of certain low molecular weight, thermally stable additives.